1. Field of the Invention
This invention relates to the manufacture of semiconductor devices, and in particular to a method of conditioning a polishing pad used in chemical mechanical polishing (CMP).
2. Description of Related Art
Fabrication of semiconductor integrated circuits (IC) is a complicated multi-step process creating microscopic structures with various electrical properties to form a connected set of devices. As the level of integration of IC's increases, the devices become smaller and more densely packed, requiring more levels of photolithography and more processing steps. As more layers are built up on the silicon wafer, problems caused by surface non-planarity become increasingly severe and can impact yield and chip performance. During the fabrication process, it may become necessary to remove excess material in a process referred to as planarization.
A common technique used to planarize the surface of a silicon wafer is CMP. CMP involves the use of a polishing pad affixed to a circular polishing table and a holder to hold the wafer face down against the rotating pad. A slurry containing abrasive and chemical additives are dispensed onto the polishing pad. The pad itself is typically chosen for its ability to act as a carrier of the slurry and to wipe away the grit and debris resulting from the polishing action.
The wafer and the polishing pad rotate relative to each other. The rotating action along with the abrasive and chemical additives of the slurry results in a polishing action that removes material from the surface of the wafer. Protrusions on the surface erode more efficiently than recessed areas leading to a flattening or planarization of the wafer surface.
A key factor in maintaining the performance and longevity of the CMP apparatus is conditioning the polishing pad. Typically the polishing pad is comprised of blown polyurethane with a felt surface layer containing many small pores to facilitate the flow of slurry to beneath the wafer being polished. There are fibers of the polyurethane which are substantially perpendicular to the surface of the polishing pad. An example of such a polishing pad is the model IC-1000 manufactured by the Rodel Corporation, 945 East San Salvador Drive, Scottsdale, Ariz. 85258.
As the number of wafers polished increases, the polishing pad becomes filled with debris formed by the accumulation of chemical reaction products and abrasives from the slurry. This causes the polishing pad to become matted down or to wear unevenly, also known as the "glazing effect". Thus, it becomes necessary to restore the polishing pad to a state suitable for continued wafer polishing.
A type of pad conditioner known in the art is a stationary conditioner mounted to the polishing pad. The roughening surface of the conditioner, also known as a grit, is in contact with the polishing pad surface. An example of such a grit is a diamond planar grinding disc, 70 .mu.m diamond, manufactured by Buehler, Microstructure Analysis Division, 41 Waukegan Road, Lake Bluff, Ill. 60044, Part No. 46-4316.
An example of a pad conditioner can be found in U.S. Pat. No. 5,785,585 issued on Jul. 28, 1998, and assigned to the assignee of the present invention. Common problems associated with such stationary pad conditioners are the buildup of slurry along one edge of the conditioner, and the buildup of debris in the grit. This causes an accelerated decline in polishing rates and uniformity.
A prior art solution to overcome the problem of debris buildup in the stationary conditioner grit is to stop the polisher and manually scrub the pad debris from the grit after every 4 to 5 wafers. This increases the polishing cycle time for polishers using this type of pad conditioner.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a method of refreshing the pad conditioner in-situ to enhance pad conditioning.
It is another object of the present invention to provide a method of polishing a semiconductor wafer.
A further object of the invention is to provide an improved in-situ pad conditioning process for CMP.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.